Plot-wise, there wasn't a whole lot of forward momentum on the fourth episode of the fourth season. The majority of the episode concerned the two groups who had left the prison in order to find medicine for the flu-stricken populace. After a detour brought about by the hundreds of walkers clogging the interstate, the Darryl, Michonne, Bob and Tyreese group finally made it to the veterinary college to find the medicine. Meanwhile, Rick and Carol hit up a local suburb for their own supply run. Some walkers were killed, some guest stars were killed and by episode's end, everyone was zipping back to the prison in their cars. (Including Rick in his astoundingly clean, kiwi green Hyundai Tucson, the car advertised heavily during the series).

But that was all on the surface. On a character level, some major shifts were taking place, including a much clearer vision of just how much Carol had changed since the apocalypse took place. For the first three episodes, we'd seen a much harder, survival-minded, Sarah Connor version of Carol, but with the revelation that she had killed flu-wracked David and Karen in secret, we see just how cold-blooded Carol had become.

As Carol explained to a young girl who was scared of turning into a walker, "You fight and fight and one day... you change. We all change."

Carol has definitely changed, and that became completely clear to Rick and the viewer in this episode. And now she's out of the group, left to fend for herself in a less-clean, non-Hyundai car. Is this the last we'll see of the woman who was Daryl's sole soft spot? Doubtful. The Governor is out there and now Carol is out there, and considering they brought back the guy we met briefly in the very first episode for a return engagement, it's almost assured this isn't the last we'll see of Carol. The only question is if this falling-out with Rick will mean she's now a sworn enemy of the prison crew, as well.

Rick, it appears, has finally returned to his old ways. He unilaterally decided to give Carol her walking papers without so much as a nod of respect to the council that's been running the prison since Rick started up his pig farming dream. While that's enough to upset the balance of peace back at the prison, it'll surely enrage Daryl. Rick may have sent Carol away to protect her from Tyreese, who was developing a thing for Karen, but it appears the act will succeed in keeping Daryl and Tyreese from doing battle over Carol's life.

Michonne seems to have finally given up on her bloodlust to find the Governor. Which means he'll probably show up again very soon. And genial Bob finally showed his dark side, almost allowing the walkers to get him over a single bottle of booze. Daryl, incidentally, doesn't take kindly to alcoholics.

Several unanswered questions remain from the episode, not even touching on whether or not the medicine swiped from the college will actually do any good. Flu or not, is anyone else concerned about that giant herd of zombies shambling down the interstate? And will the mysterious prison member who feeds rats to walkers at the fence line ever be revealed?

And then there's the books at the veterinary college. As Michonne and the rest raided the lab for medicine, Bob spotted a cot set up with a bottle of hooch and several books, all apparently made up, with titles like "Pathology of Fear" and "Enter a New Dawn." Whose books were these? Had the owner become walker food? Or was he simply out for the afternoon? And what are we to make of those titles, which were featured prominently enough for eagle-eyed viewers to wonder about. Is this the dawning of a more "Lost"-ian "Walking Dead," filled with clues and rabbit holes for the fans to ponder? Or is it simply just a case of really, really good set dressing?

The weeks ahead will decide. One thing we're left pondering is Bob's morose confession to his companions that he's been part of two groups that didn't meet good ends. "Two times, two different groups, I was the last one standing. Like I was supposed to watch it happen over and over like a curse."

Based on the scenes from next week, it appears Bob may be present for a third group about to go down the tubes. And we'll see that Rick really did Carol a huge favor.